action: lateral flexion of the trunk; stabilizer and flexor of the hip

Gross anatomy

The psoas muscle arises from the transverse processes, lateral aspects of the vertebral bodies and intervertebral discs of the T12-L5 vertebral column. It fuses with the iliacus muscle to form the iliopsoas muscle at the level of L5-S2 and passes inferiorly, deep to the inguinal ligament, to insert into the lesser trochanter of the femur1-3.

The lumbar plexus is embedded within the muscle and its branches emerge from it 3: